Welcome to our weekly newsletter where we highlight environmental trends and solutions that are moving us to a more sustainable world.

Hey, I'm Alexandra. When we came across this story about eels dying in droves at hydro dams, our first thought was: if this was birds and windmills, there'd be an uproar. Our slippery friends deserve to navigate their waterways safely. Here's a company that's working on a tech solution to this problem. This week: Eels keep dying in hydro dam turbines. A new design could change that The Big Picture: How a heat pump works Why an airship was spotted hovering over this central Alberta town Eels keep dying in hydro dam turbines.

A new design could change that American eels have to pass through the blades of hydropower plant turbines as they migrate down the St. Lawrence River, a perilous journey that has only a 74 per cent survival rate at one power plant. New turbine runners could change that, Natal Energy says. (Stephany Hildebrand) Every year, thousands of endangered American eels swim down the St. Lawrence River on their way to their breeding grounds in the Sargasso Sea in the Caribbean.

But many of them are struck and killed by the turbine blades of the hydroelectric dams spanning the river, one factor contributing to a 99 per cent population decline in the area since the 1970s.

Researchers at Natel Energy, a California startup specializing in fish-friendly turbines, say they’ve designed a turbine runner that would stop those fatalities — without sacrificing power generation efficiency.

“For many decades, people thought that if you were going to protect fish, you're going to lose power, or you're going to incur some large civil work expenditure,” Kate Stirr, Natal Energy's vice-president of external affairs, told CBC News.

“What's illustrated by [our] study is that there's no trade-off between power generation and fish survival that's necessary to make.”Why declining eels are a big deal American eels are Canada’s only true catadromous species, meaning they’re born in the ocean, then swim upstream to spend their adult lives in freshwater locations like Lake Ontario, sometimes for up to 20 years. Finally, after growing sometimes over a metre in length, they swim back out to the ocean to spawn.

Seen as a key indicator of the biodiversity of the region, the eel has also long been important and even sacred to Indigenous people along Lake Ontario and the St. Lawrence and Ottawa rivers. And although they’ve historically been abundant in Lake Ontario, their numbers have plummeted due to overfishing, habitat loss and hydroelectric dams. By the late 2010s, just 18,000 passed through fish ladders at the Moses-Saunders Power Dam each year on average, down from a million in the '80s. As all of the American eels in the St. Lawrence River basin are breeding females, their migration downstream is important for the success of the overall species.

Commercial fishing of eels was banned in Ontario in 2004, and various programs have attempted to combat population drops, such as one funded by Ontario Power Generation paying fishermen to trap live eels and transfer them down the river to bypass hydro plants.

Testing in the late '90s found that more than a third of the eels trying to migrate downstream were killed by hydroelectric dams on the St. Lawrence River, with turbines at the Moses-Saunders Dam alone killing roughly 26 per cent of the eels that passed through.

The dam provides power to both the U.S. and Ontario, and is one of two mainstem hydroelectric plants on the St. Lawrence that eels must survive to reach the ocean. A less deadly turbine Natel's new “FishSafe” turbine design features a more curved blade shape and a “thick, blunt leading edge” instead of a thin one, providing a more glancing blow that reduces the chance of injury if a fish is struck by the rotating blades. It also minimizes the gap between the blade and its housing to lower the chance of fish getting trapped.

A computer simulation of turbines on the U.S. side of the Moses-Saunders dam found the new design could raise the survival rate of American eels passing through to 98 per cent.

The eels in the St. Lawrence River basin are overwhelmingly breeding females, making their survival important to the overall species (Stephany Hildebrand) The new blade design also demonstrated a comparable efficiency as existing ones, and can be installed without costly full-system overhauls in most cases.

“If we can have a solution where the runner just is an in-place upgrade, then it makes it very easy for the owner to think about a solution that protects fish in addition to modernizing their plant,” Stirr said.

A lot of the existing hydropower plants in North America and in Europe are decades old, she said. Natel Energy is hoping that its new proof-of-concept will show hydro dam companies that prioritizing fish survival won’t cut into their bottom line, and convince more to come on board.

A rendering of one of Natel Energy’s FishSafe turbines. (Natel Energy) She said the firm has been in conversation with Canadian companies, and recently installed some of its turbine runners at a plant in France that was subject to regulations protecting European eels. The turbines have since been successfully tested with live eels.

“We love eels, and I would say that this technology, we hope, can really be a game-changer for the American eel population.”—Alexandra Mae Jones Old issues of What on Earth? are here . The CBC News climate page is here .

Check our podcast and radio show. In our latest episode : Alberta has the country on tenterhooks as the province votes on whether to consider splitting from Canada. At least one separatist leader says the threat to leave is serving as leverage for the oil industry. Others in the province say investment in renewable energy is already taking a hit.

This week, we’re asking how past fights over the oilsands got tangled up with separatism, what the referendum means for Alberta’s energy industry now and what an independent Alberta would mean for the climate.

What On Earth? drops new podcast episodes every Wednesday and Saturday. You can find them on your favourite podcast app or on demand at CBC Listen . The radio show airs Sundays at 11 a.m., 11:30 a.m. in Newfoundland and Labrador.

Check the CBC News Climate Dashboard for live updates on record-breaking weather and current conditions across the country. Set your location to find out how today's temperatures compare to historical trends. (CBC) Reader feedback Last week's issue included a story on why Fredericton Botanic Garden planted three ash trees upside down . The trees were among 14 removed after they were infected with emerald ash borer.

Gord Campbell wrote: "You failed to mention that there is a vaccine that can protect an ash tree for up to three years per injection, costing between $150 and $350 per tree. We have had excellent success protecting our beautiful ash for about the last 15 years. The cost of removing a dead or dying ash tree often exceeds preventive treatment."

The City of Fredericton is trying to slow the emerald ash borer beetles down with the vaccine-like insecticide TreeAzin and with pheromone traps to catch the adult beetles. But there has been debate in some cities about whether it's better to vaccinate trees, which some say is just "delaying the inevitable," or spend the same money on cutting and replacing them.

Lena Measures wrote in about balcony solar panels: "These inexpensive, easy-to-install plug-in solar panels are having a moment in Germany and starting to sell in other places such as the U.S. Some are sold at Ikea. Are they a good idea and why are they not available in Canada?"

In fact, Nick Logan wrote about that just last year. Here's what he found .

Got questions, comments or just want to share something? Write us at whatonearth@cbc.ca (and send photos there, too!) The Big Picture: How heat pumps work Green Communities Canada, a group that promotes local climate action, has named this week Heat Pump Week (coinciding with the U.K.'s National Heat Pump Week ).

And it's good timing, because the federal government just announced $2 billion in rebates for heat pumps last week. The goal is to ensure that people whose heating systems are old or breaking down don't automatically replace it with the same kind of system — in a majority of Canadian homes, that's a fossil fuel-burning furnace.

The government wants people to consider a heat pump, an efficient form of electric heating. The diagram below shows how it works. Check out these articles to learn more about heat pumps , whether they could help you save money and why you could even consider adding one to your existing heating system . Hot and bothered: Provocative ideas from around the web Why haven't more Canadians bought EVs yet? A new survey suggests they are waiting for more choice in certain kinds of electric vehicles .

Ever ask AI about advice on what to cook for dinner, what car to buy or what heating system to install? A Canadian research team looked at what advice AI chatbots gave, and found they had human-like biases that nudged people away from climate action .

One proposed solution to climate change is technologies that effectively "dim the sun," but they could have negative impacts on some parts of the world. Could countries (and other stakeholders) around the world rationally agree on how to use them, based on the best available science? A researcher ran a "war-game" simulation to find out. Here's how it went .

Energy co-operatives allow ordinary people, including those who don't own any property, to fund and own a piece of renewable energy projects, including wind, solar and biogas. Corporate Knights profiles eight such successful projects in Canada .

Before colonialism, Hawaiians raised fish for food in specially designed ponds. Yale Climate Connections looks at how the technology worked, and why groups are now trying to restore these ponds . Why an airship was spotted hovering over this central Alberta town The Rocky Mountain House Airport hosted this autonomous airship last week during trials testing a new way to collect aerial survey data. (Submitted by 3 Points in Space Media) A rare sight in the sky over central Alberta last week turned heads and had people asking: Was that really a 20-metre blimp?

While some may have seen a Goodyear Blimp at a sporting event, it’s not every day you see such a sight in rural Alberta.

In this case, it was a solar-powered airship roughly the size of a school bus, testing a new way to collect aerial survey data near Rocky Mountain House, about 200 kilometres southwest of Edmonton.

A joint crew from Cloudline, a South African aerospace firm that manufactured the airship, and its Canadian operational partner, 3 Points in Space Media, ran flight tests with the airship out of the Rocky Mountain House Airport last week.

“It's essentially the same as a helium party balloon,” said Sean Adams, founder and CEO of 3 Points in Space Media, as the crew conducted a trial with TC Energy to inspect pipeline corridors in the region.

He noted airship technology actually goes back many years, though it is doing something a little different from the blimps of the past.

“This particular technology, as far as I know, is very new,” Adams said, and combining control systems with the blimp makes it an autonomous airship. Why an airship was spotted hovering over this central Alberta town October 12|Duration 2:51A rare sight in the sky over central Alberta turned heads recently, leaving residents asking: Was that really a 20-metre blimp? CBC’s Nadeer Hashmi has the details.

Pre-flight preparation starts with crews filling the envelope with helium and running diagnostic checks while the airship remains tethered. Once cleared, Adams said operators release the aircraft for calibration runs before launching long-distance survey flights.

“We've actually just finished flying a 100-kilometre run,” Adams said, noting the airship is classified as a remotely piloted aircraft system with automated flight controls.

He said it's useful for collecting data in remote areas, such as monitoring pipelines, power lines and infrastructure. Traditionally, energy companies rely on conventional aircraft or smaller survey drones for this work.

However, Cloudline's CEO and founder Spencer Horne said the airship's 40-kilogram payload capacity allows it to carry heavier camera and LiDAR sensors over much greater distances than standard drones.

“There are now heavier lift drones that are getting into 10-, 20-, even 30-kilogram payloads,” he said. “But a very important distinction to make is that … on those aircraft, your maximum payload is happening at your minimum range.”

Still, Adams acknowledged that crewed aircraft could handle a lot more than airships when dealing with severe cold and unpredictable weather.

“Which is one of the prime use cases we're trying to develop here is to harden it so that we can use it for that,” he said.

In an emailed statement to CBC News, Joe Zhou, vice-president of pipeline integrity at TC Energy, said the research initiative creates the potential to gather multiple types of data in a single flight, adding that the approach is quieter than conventional aircraft. Local curiosity For those in the Rocky Mountain House area, seeing an airship created plenty of buzz.

“We've never seen that. Actually, I've never seen that in my lifetime. And I'm 65,” said Rocky Mountain House Mayor Shane Boniface with a chuckle.

He said that the town's communications officer noted that the airship photos got more views on Facebook than its post about a recent tornado.

While Cloudline said it operates airships internationally in countries including South Africa, Namibia and Kenya, they still remain a rare sight in Canadian airspace. That said, an autonomous hydrogen fuel-cell powered airship flew over Halifax just last week .

Next up for the flight team is cold-weather testing in northern Ontario to prepare the aircraft for sub-zero operations and Arctic conditions. — Nadeer Hashmi Thanks for reading . If y ou have questions, criticisms or story tips, please send them to whatonearth@cbc.ca . What on Earth? comes straight to your inbox every Thursday.

Editor: Emily Chung | Logo design: Sködt McNalty